Sacrificial metal pipe coverings



July 12, 1966 w. E KEMP ETAL SACRIFICIAL METAL PIPE COVERINGS FiledApril 1,, 1965 2 Sheets-Sheet l FIG. 2

FIG. 4

INVENTORS WO0DEOW E. KEMP FOBEET C. KENAN fie/r y 2, 1966 w. E. KEMPETAL SACRIFICIAL METAL PIPE COVERINGS 2 Sheets-Sheet 2 Filed April 1,1965 FIG. 5

INVENTOR. WOOD/20W E. KEMP ROBEPT C- KEN/IN BY 5 l/Ieir United StatesPatent 3,260,661 SACRIFICIAL METAL PIPE COVERINGS Woodrow E. Kemp,Pittsburgh, Pa., and Robert C. Kenan, Long Grove, Ill., assignors toKoppers Company, Inc., a corporation of Delaware Filed Apr. 1, 1965,Ser. No. 444,662 4 Claims. (Cl. 204148) This invention relates generallyto electrolysis and more particularly to apparatus and method forproviding cathodic protection to metallic structures, such as steel andiron pipe and the like and is a continuation-in-part of th inventiondescribed in application Serial No. 162,795, filed December 28, 1961,now abandoned.

Pipes or conduits that are installed underground are subjected to attackby such corrosive elements as moisture, water, oil, electrical current,bacteria, and other elements that may be present in the soil. Coal tarpitch and asphalt have long been used for the coating of gas,

' oil and water lines to give protection to such lines. Coal tar pitchis resistant to soil bacteria and soil corrosives as well as to waterbut when either coal tar pitch or asphalt has been used to coatunderground pipelines, it has not been able to minimize or prevent thedestructive effect of galvanic corrosion or stray current electrolysison the buried pipe.

It has been necessary, heretofore, to provide cathodic protection bymaking the pipe electrically negative with respect to the surroundingsoil or other structures. Conventionally, an electrical potential wasimpressed on the pipe by connecting it with an artificial supply ofdirect current at a properly controlled voltage or with a galvanic cellusing a piece of zinc and the pipe as the electrodes and the soil as theelectrolyte. These particular methods of cathodically protecting pipeare not satisfactory however, because the need of an electricalpotential by using an artificial supply of direct current requires extraequipment and a continuing source of electrical current. The use ofsingle pieces of zinc or other metals as electrodes requires extensiveengineering study to determine the number of zinc electrodes that shouldbe spaced along the pipe line to give the proper cathodic protection.This type of study can be very involved since oil and gas pipe lines,for example, stretch for hundreds of miles and this means that the pipeline will be, in soils of varying chemical and electrical makeup; thusit is difiicult to determine the proper amount of spacing of electrodes.

The heretofore known methods of providing cathodic protection to pipeincluded the application of the coal tar pitch and coal tar enamelcoatings to outer surface of the pipe. It is necessary in such methodsto heat the coal tar pitch to approximately 500 F. and the applicationof this hot pitch created handling problems and it is not convenientlypractical to place a metal electrode in the tar coating to providecathodic protection to the pipes.

In contrast to th foregoing cathodic protective methods, the presentinvention includes a method for providing cathodic protection tometallic structures such as steel pipe, structural members and the likecomprising the steps of applying to the surface of the metallicstructure a laminate structure comprised of a sacrificial anodicmetallic foil selected from the group consisting of zinc, magnesium, andzinc-magnesium alloys, and a pressure sensitive adhesive for adheringone surface of the foil and to the metallic structure comprised of coaltar pitch in quantity amounting to between 40 and 60 percent by weightof the adhesive composition and having a Brookfield viscosity at 200 F.in the range of 100 to 400, a copolymer of acrylonitrile and butadienein quantity amounting to between 0.5 and 3.0 percent by weight of theadhesive composition and having a Mooney viscosity 3,260,661 PatentedJuly 12, 1966 "ice v in th range of 25 to 175, polyisobutylene inquantity amounting to between 30 and 50 percent by weight of theadhesive composition and having a molecular weight in the range of 7,000to 15,000, and fibrous, hydrous magnesium silicate in quantity amountingto between Zero and 20 percent by weight of the adhesive composition andhaving a specific gravity of about 2.5, an oil absorption in the rangeof 34 to 44, and a particle size such that between 50 and 60 percentpasses through a United States standard No. 140 screen, and electricallybonding said anodic lamina to said metallic structure.

For a further understanding of the present invention and for furtheradvantages and features thereof, reference may be made to the followingdescription taken in conjunction with the accompanying drawings whichshow for the purpose of exemplification, embodiments of the invention.

In the drawings:

FIG. 1 is a schematic view of one embodiment of the laminate structureof the invention being applied in one manner to a length of pipe;

FIG. 2 is a schematic view of a preferred first embodiment of thelaminate structure of the invention;

FIG. 3 is a schematic view of the laminate structure of the inventionbeing applied in another manner to a length of pipe;

FIG. 4 is a schematic view of a second embodiment of the laminatestructure of the present invention;

FIG. 5 is a schematic view of a third embodiment of the presentinvention being applied to a portion of a length I of pipe;

FIG. 6 is a schematic view of a fourth embodiment of the presentinvention being applied to a portion of a length of pipe;

FIG. 7 is a schematic view of a fifth embodiment of the presentinvention being applied to a portion of a length of pipe;

FIG. 8 is a sectional view along line VIII-NIH of FIG. 5; and

FIG. 9 is a sectional view along line IXIX of FIG. 3.

In FIG. 1, a length of pipe 10, which may either be steel or iron orother metal which is subject to corrosive attack, is being coated with alaminate 9 in' the form of a sleeve split lengthwise so as to embracethe pipe 10.

FIG. 2 illustrates a preferred first embodiment of the laminate 9 whichcomprises an outer environmental protective layer 7 applied to anadhesive coated sacrificial anodic metallic layer 6. The surfaces of theanodic metallic layer are coated with an adhesive 8 which is preferablya coal tar pitch, pressure-sensitive type adhesive. The exposed surfaceof the adhesive layer 3 is covered with a conventional type of siliconetreated re lease paper layer 2. The sacrificial anodic metallic layer 6is preferably either zinc or magnesium, or an alloy thereof.

The laminate 9 or adherend is comprised of materials which are flexibleand readily conformable to the surface of another adherend, such asmetal structures including pipes, structural members and the like. Thelaminate 9 is comprised of selected materials having the requisitecharacteristics for cathodically portecting underground meter ofthickness.

or an alloy of these metals.

volts per millimeter of thickness permits the anodic metal lic layer 6to be consumed rapidly, because the current loss resulting from theelectrical resistance to current flow would be extremely high. Adielectric strength greater than 1,000 volts per millimeter of thicknesshas no practical advantage in the novel laminate of this invention sincethe electrical currents encountered are not expected to be high enoughto Warrant use of such material.

The dielectric material layer 7 should be flexible. If the dielectricmaterial can be bent on a 1 inch diameter mandrel, through an arc of 180Without cracking it is suitable. The dielectric material should bemoisture-resistant. If the material absorbs more than 8 percent ofwater, electrical currents would then be conducted directly to thepipeline and cause corrosion deterioration. The dielectric material,when used in thicknesses under 50 millimeters, should have a moisturevapor transfer rate of less than 1 perm, measured in accordance withspecification ASTM No. E96-53T. Examples of some materials suitable forthe dielectric layer are: polyethylene, polyvinylchloride, asphalt, andcoal tar pitch.

The release paper layer 2 is a conventional material, such as siliconetreated film or paper which readily adheres to the adhesive compositionlayer 8, but which may also be readily stripped off, leaving theadhesive composition with sufficient tackiness to form \an instantaneousstrong bond to whatever surface it is thereafter applied.

FIG. 4 illustrates a second embodiment of the laminate in the form of atape 9a, and the sacrificial anodic metallic layer 6 is in the form. ofa foil mesh such as wire mesh. The foil mesh material is preferably zincor magnesium The general construction of the laminate 9a is the same asthe laminate 9 except for the form of the sacrificial anodic metalliclayer 6.

FIG. 5 illustrates a third embodiment of the laminate, in the form of atape 9b, and the sacrificial anodic metallic layer 6 in this instance isthe outermost layer. The dielectric layer 7, in this embodiment, isinterposed between the anodic layer 6 and the surface of the pipe 10.The layers 6 and 7 are maintained in spaced apart relation and areadhesively secured to each other and to the pipe by the adhesive layers8, interposed in the manner shown. The release paper layer 2 in thesecases is shown partially removed.

It is desirable and necessary to electrically connect the anodicmetallic layer 6 to the pipe 10. This may be accomplished in anysuitable manner. One such way is to insert a U-shaped clip 12 of copperfoil or other electrically conductive material, into the tape 9b so thatthe copper foil 12 contacts both the anodic metallic layer 6 and thepipe 10. FIG. 8 shows one such copper foil 12 inserted in the tape 9b toelectrically connect the metallic foil 6 and the surface of the pipe 10.

FIG. 6 illustrates a fourth embodiment of the laminate in the form of atape 90 comprised of a sacrificial anodic metallic layer 6, which is theoutermost layer in this instance, an adhesive layer 8 and a conventionalsilicone treated release paper layer 2 that is partially removed. Itwill be noted also that the anodic metallic layer 6 is likewiseelectrically connected to the metallic pipe 10 by one of the U-shapedcopper foil clips. 12. In most instances the U-shva-ped copper clips maybe inserted into the adhesive 8 at the interface between it and themetallic foil 6. The clip may be easily folded over the lower suface ofthe adhesive layer 8, as shown in FIGS. 8 and 9 whereby a,

satisfactory electrical conductive path is established between thean-odic layer 6 and the metal pipe 10.

FIG. 7 illustrates a fifth embodiment of the laminate, in the form of atape 9d, comprised of the usual sacrificial anodic metallic layer 6,forming the outer layer, superposed on a layer 11 of coal tar pitchwhich is adhesively secured to an adhesive layer 8. When applied to thepipe 10, the conventional release paper layer 2 is removed, as shown,and one of the U-shaped copper foil clips 12 is inserted to provide anelectric connection between the anodic layer 6 and the surface of thepipe 10.

FIG. 3 illustrates the copper foil clip 12 installed at the end of onelength of the present laminate tape 13 and adjacent the beginning ofanother length of laminate 130. It is desirable and convenient to insertthe COPPEI foil clips 12 adjacent the end of one length of tape or atthe commencement of another length of tape. However, the U-shaped copperfoil clips 12 may be inserted along a length of tape whenever desirableor necessary.

It is important that the several embodiments of the laminate 9 beprepared in such a manner that the anodic metallic foil or mesh is nevercontiguous with the pipe to be protected. This for the reason that, if asmall puncture or hole is made in the laminate, water can seep throughthe laminate and reach the pipe surface. Corrosive activity will resultand there will then be a continuous deposition of corrosive products atthe interface of the laminate and the pipe.

FIG. 1 illustrates one method for cathodically protecting a length ofpipe using the laminate of the present invention. The method comprisesthe steps of: (1) cutting a strip of laminate 9, preferably in the formof a tape having a Width substantially equal to the circumference of thepipe 10 and a length substantially equal to the length of the pipe; (2)removing the release paper layer 2; (3) placing the strip of laminatelengthwise on the pipe with the adhesive layer 8 against the outer pipesurface; (4) Wrapping the laminate around the pipe so that thelongitudinal edges of the laminate either abut or slightly overlap andform a single lengthwise seam; and then (5) heat sealing thelongitudinal seam by means known in the art.

FIG. 3 illustrates another method for cathodically pro- I tecting alength of pipe by spirally wrapping it with the protective laminate 9 inthe form of tapes 13, 13a. The laminate 13, 13a may of course have anysuitable widths. The tapes 13, 13a also may have any one of thestructures shown and described hereinbefore, and be wrapped around pipespirally in such a manner that the edges of adjacent convolutions abutor slightly overlap. Of course, before the tape is wrapped on the pipe,the release paper layer 2 is removed. The adhesive quality of theparticular coal tar pitch adhesive layer 8 provides satisfactoryeffective adhesion not only to the pipe surface, but also with theadjacent abutting spiral convolution. Thus, when adjacent convolutionsare pressed against one another during the application of the tape, theabutting adhesive layers 8 tend to cold flow together and form a singlehomogeneous adhesive layer. There is no need to heat seal the outerlayer or any part of the laminate tape unless such action is preferred.

The cathodic protective characteristics of the laminate tape may in someinstances, be further improved by placing the anodic metallic foil ormesh 6 on the exterior of the laminate as shown in FIGS. 5-7. The metalfoil or mesh 6 is made of a suitable metal which is anodic to thematerial of the object to be protected. Generally, the anodic metal foilor mesh will be either Zinc or magnesium, or a zinc-magnesium alloy andthe metal to be protected will be steel. Such sacrificial anodic foil ormesh materials have excellent electrical conducting characteristics andstray electrical currents will not cause galvanic or electrolyticcorrosion of the pipe. Moveover, in the unlikely event that moisturewould reach the pipe through a hole or a puncture in the protectivecoating, corrosion of the metal pipe would not take place, because, atselected strategic locations along the length of pipe the copper foils12 are connected between the metal pipe and the anodic metal foil layer6.

Several samples of the laminate of this invention were prepared andcoated onto steel pipe. For each sample, the position of the zinc anodewas varied and the type of dielectric material used was also varied.Each of these coated pipes consisted of 2 /2" diameter by 1 long mildspecifically described in Table I which is set out below,-

the adhesive material used was prepared according to the descriptiongiven as follows.

EXAMPLE I 40 parts of heavy creosote oil are added to 30 parts of coaltar pitch. The temperature of this mixture is raised to 350 F. (1 hr.)and 30 parts of pulverized coal added. The mixture is then placed in anagitated still and heated to a temperature of 600 F. and held at thistemperature for 1 hour or until the coal dissolves. The mixture is thencooled for 2 to 3 hours to 300 F. and 5 parts of a medium molecularweight copolymer of butadiene and acrylonitrile (75:25 ratio), and 30parts of heavy creosote oil are added. The mixture is then maintained at300 F. for four hours. Thereafter, 35 parts of ball clay are added andmixed for three hours.

The resulting composition is a black, thick, creamy material having aviscosity at 250 F., using a Brookfield viscometer, model LVF spindlenumber 4, 12 r.p.m., of between 20,000 and 40,000 centipoises, and apenetration of 100-140 mm. at 77 F. (50 gms.; 5 seconds) ASTM D5 and aring and ball softening point of 45 C. to 55 C.

The composition, as prepared in this example, was applied to a steelI-beam of the type used in construction. Subsequently, the thus-coatedI-beam was further encapsulated in concrete. The composition adheredcompletely to both the metal beam and to the concrete cover, preventingany deterioration or corrosion of the metal beam by the action of thecorrosive agents present in concrete. The composition of this examplecan be similarly applied to other metal construction materials which areto be coated with concrete, such as aluminum.

TABLE I.LAMINATE COMPOSITION IN THE ORDER OF MATERIAL LOCATION TO THEPIPE SUBSTRATE The above samples were removed from the sea water after 4months exposure. The samples were then checked for corrosion in theareas adjacent to the deliberate punctures. No corrosion was observed.Each of the puncture areas was covered with a white deposite whichconsisted of a cathodically deposited calcareous coating resulting fromsea water decomposition and from some anodic zinc corrosion product. Thepipes were completely free of corrosion and the coating compositionsshowed no damage.

Another adhesive composition of the pressure-sensitive type, which hasbeen found to be exceptionally effective for the purpose of adhering thesacrificial anodic metallic lamina to a metallic surface subject tocorrosive attack, comprises a mixture of coal tar pitch, a copolymer ofacrylontrile and butadiene, polyisobutylene and fibrous hydrousmagnesium silicate.

Such adhesive composition is described in a copending application SerialNo. 442,073, filed March 23, 1965. Generally, the adhesive is formulatedin the following manner:

(a) Heating to 275 F. a quantity of coal tar pitch amounting to between40 and 60 percent by weight of the adhesive composition and having aBrookfield viscosity at 200 F. in the range of -400;

(b) Adding to and mixing with said coal tar pitch at 275 F. a quantityof a copolymer of acrylonitrile and butadiene amounting to between 0.5and 3.0 percent by weight of the adhesive composition and having aMooney viscosity in the range of 25-175, until said copolymer isdispersed or dissolved and the mixture is homogeneous and free of lumps;

(c) Adding to said mixture and mixing therewith a quantity ofpolyisobutylene amounting to between 30 and 50 percent by weight of theadhesive composition and having a molecular weight in the range of10,000-12,000, until the mixture is smooth again; and

(d) Adding to the mixture and thoroughly mixing therewith a quantity offibrous hydrous magnesium silicate amounting to between Zero and 20percent by weight of the adhesive composition and having a specificgravity of about 2.5, an absorption in the range of 34-44 pounds of oilper one hundred pounds of pigment, and a particle size such that between50 and 60 percent thereof passes through a United States standard No.screen, until a smooth thixotropic product is produced.

It is generally desirable to cover the exposed surface of the adhesivewith a silicone treated release paper layer 2 until it is ready forapplication. When ready for use the silicone treated release paper ofcourse is removed. Such release papers are conventional and prevent theseveral configurations of the tape, when made and stored, from stickingtogether.

In contrast to known methods and apparatus to cathodically protectmetallic structures such as pipe, the applicants have provided a novellaminar structure which can be simply and easily applied to a pipe. Itis only necessary to remove the release paper layer and then wrap thetape around the object to be protected, inserting from time to time thecopper foils 12. Such a structure is both simple to use and highlyeffective in service.

If the cathode is a length of pipe, for example, the preferred manner ofapplying the cathodic protective laminate is to spirally wind the tapeon the pipe making sure that adjacent convolutions are edge abutting orslightly overlap. If the cathode is a structural member, such as anI-beam, channel, angle and the like, the preferred manner of applyingthe cathodic protective laminate is to apply lengths of the tape to thesurface of the structural member making sure that adjacent lengths areedge abutting or slightly overlapping. The entire surface of the cathodein the area subject to corrosive attack should be protected with thelaminate.

From the foregoing it should be apparent that the cathodic protectivelaminate of the present invention has many features and advantages notheretofore available, such as, continuity of protection, ease ofapplication, effectiveness and simplicity.

We claim:

1. The method to cathodically protect a metallic structure comprisingthe steps of:

(a) providing a laminate structure comprised of (l) a sacrificial anodicmetallic foil lamina selected from the groupconsisting of zinc,magnesium, and zinc-magnesium alloys;

(2) pressure sensitive adhesive laminae applied to opposed surfaces ofsaid foil lamina, one of said adhesive lamina adhering the anodic foillamina to and maintaining said foil in spaced apart relation to thesurface of said metallic structure, said adhesive being comprised of (a)coal tar pitch in quantity amounting to between 40 and 60 percent byweight of the adhesive composition and having a Brook- 'field viscosityat 200 F. in the range of 100 to 400; (b) a copolymer of acrylonitrileand butadiene in quantity amounting to between 0.5-

and 3.0 percent by weight of the adhesive composition and having aMooney viscosity in the range of 25 to 175;

(c) polyisobutylene in quantity amounting to between 30 and 50 percentby weight of the adhesive composition and having a molecular weight inthe range of 7,000 to 15,000; and

(d) fibrous, hydrous magnesium silicate in quantity amounting to betweenzero and percent by weight of the adhesive composition and having aspecific gravity of about 2.5, an oil absorption in the range of 34 to44 pounds of oil per one hundred pounds of pigment, and a particle sizesuch that between 50 and 60 percent passes through a United Statesstandard No. 140 screen;

(3) an outermost flexible environmental protective dielectric laminaapplied to and adhering to the other adhesive lamina on said anodic toillamina;

(b) applying said laminate structure to the metallic structure so thatthe pressure sensitive adhesive lamina adheres to the surface of themetallic structure; and

(c) electrically connecting said anodic lamina to said metallicstructure.

2. The method to cathodically protect a metallic structure comprisingthe steps of;

(a) providing a laminate structure comprised of:

( 1) an outer sacrificial anodic metallic foil lamina selected from thegroup consisting of zinc, magnesium, and zinc-magnesium alloys;

(2) a next adjacent intermediary lamina comprised of coal tar pitchadhering to said foil lamina;

(3) a next adjacent innermost lamina comprised of a pressure sensitiveadhesive for adhering the outer laminates to said metallic structure andbeing comprised of (a) coal tar pitch in quantity amounting to between40 and 60 percent by weight of the adhesive composition and having aBrook- -fie1d viscosity at 200 F. in the range of 100 to 400;

(b) a copolymer of acrylonitrile and butadiene in quantity amounting tobetween 0.5 and 3.0 percent by Weight of the adhesive composition andhaving a Mooney viscosity in the range of to 175;

' (c) polyisobutylene in quantity amounting to between and 50 percent byweight of the adhesive composition and having a molecular weight in therange of 7,000 to 15,000; and

(d) fibrous, hydrous magnesium silicate in quantity amounting to betweenzero and 20 percent by weight of the adhesive composition and having aspecific gravity of about 2.5, an oil absorption in the range of 34 to44 pounds of oil per one hundred pounds of pigment, and a particle sizesuch that between 50 and 60 percent passes through a United Statesstandard No. 140 screen;

'(b) applying said laminate structure to the metallic structure so thatthe pressure sensitive adhesive lamina adheres to the surface of themetallic structure; and

(c) electrically connecting said anodic lamina to said metallicstructure.-

3. The method to cathodically protect a metallic structure comprisingthe steps of:

(a) providing a laminate structure comprised of 1) an outermost flexibleenvironmental protective dielectric lamina;

(2) a sacrificial anodic metallic foil mesh lamina selected from thegroup consisting of zinc, magnesium, and zinc-magnesium alloysinterposed in spaced apart relation to said dielectric lamina and saidmetallic structure;

(3) a first adhesive lamina coating said anodic metallic mesh lamina andadhering the same to said dielectric lamina;

(4) a second adhesive lamina coating said anodic metallic mesh laminaand adhering the same to and maintaining the same in spaced apartrelation to said metallic structure, said adhesive laminae beingcomprised of (a) coal tar pitch in quantity amounting to between 40 and60 percent by weight of the adhesive composition and having a Brookfieldviscosity at 200 F. in the range of to 400;

(b) a copolymer of acrylonitrile and butadiene in quantity amounting tobetween 0.5 and 3.0 percent by weight of the adhesive composition andhaving a Mooney viscosity in the range of 25 to 175;

(c) polyisobutylene in quantity amounting to between 30 and 50 percentby weight of the adhesive composition and having a molecular weight inthe range of 7,000 and 15,000; and

(d) fibrous, hydrous magnesium silicate in quantity amounting to betweenzero and 20 percent by weight of the adhesive composition and having aspecific gravity of about 2.5, an oil absorption in the range of 34 to44 pounds of oil per one hundred pounds of pigment, and a particle sizesuch that between 50 and 60 percent passes through a United Statesstandard No. screen;

(b) applying said laminate structure to the metallic structure so thatthe pressure sensitive adhesive lamina adheres to the surface of themetallic structure; and

(c) electrically connecting said anodic lamina to said metallicstructure.

4. The method to cathodically protect a metallic structure comprisingthe steps of:

(a) providing a laminate structure comprised of (1) an outer sacrificialanodic metallic foil lamina selected from the group consisting of zinc,magnesium, and zinc-magnesium alloys;

(2) a flexible dielectric lamina interposed in spaced apart relation tosaid anodic metallic foil lamina and said metallic structure;

(3) a first adhesive lamina adhering said dielectric lamina to saidanodic metallic foil lamina; and

(4) a second adhesive lamina coating said dielectric lamina and adheringthe same to and maint-aini-ng-the outer laminae in spaced apart relationto said metallic structure, said adhesive laminae being comprised of (a)coal tar pitch in quantity amounting to between 40 and 60 percent byweight of the adhesive composition and having a Brookfield viscosity at200 F. in the range of 100 to 400;

(b) a copolymer of acrylonitrile and butadiene in quantity amounting tobetween 0.5 and 3.0 percent by weight of the adhesive composition andhaving a Mooney viscosity in the range of 25 to (c) polyisobutylene inquantity amounting to between 30 and 50 percent by Weight of theadhesive composition and having a molecular weight in the range of 7,000to 15,000; and

(d) fibrous, hydrous magnesium silicate in quantity amounting to betweenzero and 20 percent by Weight of the adhesive composition and having aspecific gravity of about 2.5, an oil absorption in the range of 34 to44 pounds of oil per one hundred pounds of pigment, and a particle sizesuch that between 50 and 60 percent passes through a United Statesstandard No. 140 screen;

(b) applying said laminate structure to the metallic structure so thatthe pressure sensitive adhesive lamina adheres to the surface of themetallic structure; and

(c) electrically connecting said anodic lamina to said metallicstructure.

References Cited by the Examiner UNITED STATES PATENTS 12/1941 Andrus204-197 12/1949 Stearns 204-196 9/1956 P-reiser 204-197 8/1957Phillipsen 161-167 4/1964 Lane et a1. 117-127 5/1965 Sheehan 156-190 8/1965 Canevari 204-148 FOREIGN PATENTS 7/ 1957 France. 9/ 1939 Germany.

15 JOHN H. MACK, Primary Examiner.

HOWARD S. WILLIAMS, Examiner.

T. TUNG, Assistant Examiner.

1. THE METHOD TO CATHODICALLY PROTECT A METALLIC STRUCTURE COMPRISINGTHE STEPS OF: (A) PROVIDING A LAMINATE STRUCTURE COMPRISED OF (1) ASACRIFICAL ANODIC METALLIC FOIL LAMINA SELECTED FROM THE GROUPCONSISTING OF ZINC, MAGNESIUM, AND ZINC-MAGNESIUM ALLOYS; (2) PRESSURESENSITIVE ADHESIVE LAMINAE APPLIED TO OPPOSED SURFACE OF SAID FOILLAMINA, ONE OF SAID ADHESIVE LAMINA ADHERING THE ANODIC FOIL LAMINA TOAND MAINTAINING SAID FOIL IN SPACED APART RELATION TO THE SURFACE OFSAID METALLIC STRUCTURE, SAID ADHESIVE BEING COMPRISES OF (A) COAL TARPITCH IN QUANTITY AMOUNTING TO BETWEEN 40 AND 60 PERCENT BY WEIGHT OFTHE ADHESIVE COMPOSITION AND HAVING A BROOKFIELD VISCOSITY AT 200*F. INTHE RANGE OF 100 TO 400; (B) A COPOLYMER OF ACRYLONITRILE AND BUTADIENEIN QUANTITY AMOUNTING TO BETWEEN 0.5 AND 3.0 PERCENT BY WEIGHT OF THEADHESIVE COMPOSITION AND HAVING A MOONEY VISCOSITY IN THE RANGE OF 25 TO175; (C) POLYISOBUTYLENE IN QUANTITY AMOUNTING TO BETWEEN 30 AND 50PERCENT BY WEIGHT OF THE ADHESIVE COMPOSITION AND HAVING A MOLECULARWEIGHT IN THE RANGE OF 7,000 TO 15,00; AND (D) FIBROUS, HYDROUSMAGNESIUM SILICATE IN QUANTITY AMOUNTING TO BETWEEN ZERO AND 20 PERCENTBY WEIGHT OF THE ADHESIVE COMPOSITION AND HAVING A SPECIFIC GRAVITY OFABOUT 2.5, AN OIL ABSORPTION IN THE RANGE OF 34 TO 44 POUNDS OF OIL PERONE HUNDRED POUNDS OF PIGMENT, AND A PARTICLE SIZE SUCH THAT BETWEEN 50AND 60 PERCENT PASSES THROUGH A UNITED STATES STANDARD NO, 140 SCREEN;(3) AN OUTERMOST FLEXIBLE ENVIRONMENTAL PROTECTIVE DIELECTRIC LAMINAAPPLIED TO AND ADHERING TO THE OTHER ADHESIVE LAMINA ON SAID ANODIC FOILLAINA; (B) APPLYING SAID LAMINATE STRUCTURE TO THE METALLIC STRUCTURE SOTHAT THE PRESSURE SENSITIVE ADHESIVE LAMINA ADHERES TO THE SURFACE OFTHE METALLIC STRUCTURE; AND (C) ELETRICALLY CONNECTING SAID ANODICLAMINA TO SAID METALLIC STRUCTURE.